SNAA400 March   2025 CDC6C , LMK6C , LMK6D , LMK6H , LMK6P

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2BAW Overview
    1. 2.1 BAW Oscillator Advantages
    2. 2.2 BAW Oscillator Overview
  6. 3LMK6C Clocking Sitara AM64 Jitter Test
    1. 3.1 Jitter Test Set Up
  7. 4Generic Guide for Clocking AM6x and TDA4x Families
  8. 5Summary
  9. 6References

3.1 Jitter Test Set Up

On the TMDS64EVM a 25MHz LVCMOS oscillator is used as an input to a CDCLVC1310 clock buffer, which is then fed into EXT_REFCLK 1 of the AM64x device. This external refclk is the frequency reference for the internal PLL and clock distribution path. The AM64x device is then configured to route the internal system clock through the output of a GPO pin. The output clock phase noise performance is measured on a phase noise analyzer, and the time-domain jitter characteristics are measured using a DPOJET tool on an oscilloscope.

Jitter performance was measured using both a quartz oscillator to generate the 25MHz refclk as well as the LMK6C BAW oscillator. With LMK6C, the output clock had a 10 to 15dB noise reduction in the frequency band of approximately 100Hz to 500kHz. Spurious tones in the range of 10kHz to 100kHz are mostly likely the result of frequency mixing with other high-frequency noise sources, such as switching voltage regulators. Spurious tones had the same power with both reference frequency sources. Time-domain jitter also showed improvements with LMK6C, especially in terms of cycle-cycle jitter.

Quartz Test Block Diagram Figure 3-1 Quartz Test Block Diagram
LMk6C Test Block Diagram Figure 3-2 LMk6C Test Block Diagram
Quartz Oscillator GPO7 Phase Noise Plot Figure 3-3 Quartz Oscillator GPO7 Phase Noise Plot
LMK6C Oscillator GPO7 Phase Noise Plot Figure 3-4 LMK6C Oscillator GPO7 Phase Noise Plot
Table 3-1 Jitter Performance Comparison
Quartz (ps) LMK6C (ps) Quartz and LMK6C Delta (ps)
RMS Jitter 45.7694 20.0778 25.6916
Period Jitter (pk – pk) 59.265 59.126 0.139
Period Jitter (std. dev) 6.7860 6.4285 0.3575
N-cycle Jitter (pk-pk) 170.49 151.05 19.44
N-cycle Jitter (std. dev) 18.695 16.896 1.799